Multi-plate and other types of hot melt adhesive or other thermoplastic material dispensing systems are well known in the fluid dispensing art and industry. Examples of United States Patents disclosing such hot melt adhesive or other thermoplastic material dispensing systems include U.S. Pat. No. 6,051,180 which issued to Kwok on Apr. 18, 2000, U.S. Pat. No. 5,904,298 which issued to Kwok et al. on May 18, 1999, U.S. Pat. No. 5,902,540 which issued to Kwok on May 11, 1999, U.S. Pat. No. 5,882,573 which issued to Kwok et al. on Mar. 16, 1999, and U.S. Pat. No. 5,862,986 which issued to Bolyard, Jr. et al. on Jan. 26, 1999. It is noted further that these patents are directed toward different types of hot melt adhesive dispensing systems, such as, for example, meltblowing, spray pattern dispensing, and the like.
As exemplified by means of U.S. Pat. No. 5,904,298 which issued to Kwok et al., the disclosed hot melt adhesive or other thermoplastic material dispensing system comprises a dual-component hot melt adhesive or other thermoplastic material dispensing system wherein two fluid flows are able to have their fluids dispensed from a plurality of output nozzles or orifices which are arranged within a transversely disposed array of output nozzles or orifices extending across the lateral extent of the nozzle or die assembly which is fluidically connected to a common manifold or head. In conjunction with such dual-component hot melt adhesive or other thermoplastic material dispensing systems, it is sometimes desired to dispense different volumes of one or both of the fluid flows depending upon the particular or predetermined hot melt adhesive or other thermoplastic material distribution or application pattern parameters to be achieved. In connection with such a dual-components variable volume hot melt adhesive or other thermoplastic material dispensing system, the two fluid flows to the transversely arrayed dispensing nozzles or orifices are respectively controlled by means of two volume control valves. Accordingly, it can be appreciated that with respect to volume deposition of the hot melt adhesive or other thermoplastic material onto an underlying substrate, six potential volume deposition states are possible. The first volume deposition state that can occur is where both of the volume control valves are closed whereby the volume of hot melt adhesive or other thermoplastic material that is dispensed onto the substrate is zero. The second volume deposition state that can occur is where the first volume control valve is open while the second volume control valve is closed whereby the volume of hot melt adhesive or other thermoplastic material that is dispensed onto the substrate is the volume of fluid controlled by means of the first volume control valve. The third volume deposition state that can occur is where the first volume control valve is closed while the second volume control valve is open whereby the volume of hot melt adhesive or other thermoplastic material that is dispensed onto the substrate is the volume of fluid controlled by means of the second volume control valve. The fourth volume deposition state that can occur is where the first volume control valve is maintained open while the second volume control valve is cyclically opened and closed whereby the volume of hot melt adhesive or other thermoplastic material that is dispensed onto the substrate comprises the volume of fluid controlled by means of the first volume control valve to which is added or superimposed in a cyclical or intermittent manner, onto the volume of hot melt adhesive or other thermoplastic material controlled by means of the first volume control valve, the volume of hot melt adhesive or other thermoplastic material controlled by means of the second volume control valve. The fifth volume deposition state that can occur is where the second volume control valve is maintained open while the first volume control valve is cyclically opened and closed whereby the volume of hot melt adhesive or other thermoplastic material that is dispensed onto the substrate comprises the volume of fluid controlled by means of the second volume control valve to which is added or superimposed in a cyclical or intermittent manner, onto the volume of hot melt adhesive or other thermoplastic material controlled by means of the second volume control valve, the volume of hot melt adhesive or other thermoplastic material controlled by means of the first volume control valve. Lastly, the sixth volume deposition state that can occur is where both of the volume control valves are open whereby the volume of hot melt adhesive or other thermoplastic material that is dispensed onto the substrate comprises the combined volumes of the hot melt adhesive or other thermoplastic material as controlled by both of the volume control valves.
While this conventional system admittedly functions satisfactorily, some operational difficulties and drawbacks have been experienced and noted. More specifically, during the aforenoted fourth and fifth operational states, hydraulic conditions can be such as to effectively be detrimental to the desired depositional results. For example, in connection with the fourth operative state, a first volume of hot melt adhesive is being continuously supplied from the first fluid flow path as a result of the first control valve being maintained open, however, a second volume of hot melt adhesive is effectively being superimposed onto the first volume of hot melt adhesive, from a second fluid flow path, as a result of the cyclical opening and closing of the second control valve. It has been experienced that when the second control valve is closed such that the flow of the second volume of hot melt adhesive is stopped or terminated, the inertial flow of the second volume of hot melt adhesive effectively undergoes, creates, or results in a negative pressure spike or drop which can negatively impact the volume flow of the first hot melt adhesive from the first fluid flow path. This negative impact upon the volume flow of the first hot melt adhesive from the first fluid flow path has in fact manifested itself as a momentary cessation in the dispensed volume of hot melt adhesive from the lateral or transverse array of dispensing dies or nozzle assemblies, whereby a gap in the hot melt adhesive, dispensed from the lateral or transverse array of dispensing dies or nozzle assemblies, appears upon the underlying substrate. A positive pressure spike will likewise occur when one of the fluid flows, having been previously taken off-line as a result of its control valve having been closed, again comes back on-line as a result of its control valve again being opened, whereby it is needed to effectively accommodate such positive pressure spikes in order to maintain the proper volumetric fluid flow of the hot melt adhesive.
A need therefore exists in the art for a new and improved variable volume hot melt adhesive or other thermoplastic material dispensing nozzle or die assembly wherein structure is incorporated therein such that the aforenoted negative or positive pressure spikes are, in effect, isolated, reduced, or effectively attenuated over a period of time whereby gaps in the dispensed volumes of hot melt adhesive do not occur when the system experiences a negative pressure spike, and in the instance of the system experiencing a positive pressure spike, the flow of the hot melt adhesive is nevertheless likewise controlled and stabilized such that the flow of the hot melt adhesive or other thermoplastic material can continue at the desired volumetric level until the normal line pressure has again been achieved over the requisite period of time.